1. Field of the Invention
This invention relates to a sheet feeding apparatus provided in machines having a mechanism for feeding a sheet or the like, such as a computer, a copier, a facsimile, a word processor, a typewriter or the like, and more particularly, to a sheet feeding apparatus utilizing travelling vibration waves.
2. Description of the Related Art
Heretofore, this kind of apparatus was configured so as to produce travelling vibration waves in elastic members holding a sheet between them in order to feed the sheet, as disclosed in Japanese Patent Public Disclosure No. 59-177243 (1984).
The principle for feeding the sheet in the above-described disclosure will now been explained by reference to FIG. 3.
In FIG. 3, a sheet 13 is held between elastic members 11 and 12 with an appropriate pressure. A travelling flexural vibration (that is, a travelling vibration wave) is produced in each of the elastic members 11 and 12. Since it is arranged so that the spatial phase difference between the two travelling vibration waves is 180.degree., the flexural vibrations in the elastic members 11 and 12 travel so that convex portions relative to the sheet 13 of the respective waves always face each other. When a certain material particle, for example, in the convex portion on the surface of each of the elastic members 11 and 12 adjacent the sheet 13 is observed, the material particle performs a movement depicting, in general, an elliptic orbit. As for the elastic member 11, when the travelling vibration wave moves in the rightward direction, the material particle depicts a clockwise elliptic locus P.sub.1, as shown in FIG. 3. Accordingly, the direction of movement of the material particle in the convex portion is reverse to the travelling direction of the vibration for both elastic members 11 and 12. Such movements function as forces to feed the sheet 13.
On the other hand, forces to feed the sheet in the same direction as the travelling direction of the wave are produced in concave portions. However, since the pressure by these forces is smaller than that in the convex portions, frictional forces between the sheet 13 and the elastic members 11 and 12 are small, and the forces to feed the sheet are therefore small. As a result, the sum total of the forces to feed the sheet function in a direction reverse to the above-described travelling direction of the flexural vibrations.
In comparison with a sheet feeding method in which a paper feeding roller is rotated by a driving force from, for example, a motor via a transmission means, such as gears and the like, the above-described sheet feeding apparatus has the excellent feature that a highly accurate sheet feeding operation can be realized without any transmission loss due to gears and the like, since the sheet is directly fed by the vibration of the elastic members. However, with such a sheet feeding apparatus, the possibility exists that the sheet is fed in an oblique direction, or moves sideways.